This invention relates generally to an image fixing apparatus which fixes unfixed picture information image formed on a sheet of copying paper thereto, and more particularly to a so-called off-line image fixing apparatus which is disposed separately from a reproduction machine to perform only a fixing function.
FIG. 1 is a perspective view of a conventional off-line image fixing apparatus 1 with its parts being broken away to show the essential portion thereof.
The apparatus 1 includes a heating unit 3 disposed within the apparatus body 2 including a casing to heat and fuse an unfixed toner image (picture information which has been developed, but not fixed yet), a vacuum paper conveyor 4 which conveys a sheet of copying paper to the heating unit 3, and a discharger 5 which discharges the sheet, on which the picture information is fixed, from the back of the body.
The heating unit 3 includes a plate heater 6 disposed below a paper conveyance passageway shown by the arrow A and a- quartz type heater lamp disposed opposite to the heating unit 6. The sheet of copying paper on which the picture information has been fixed is discharged from the body 2 by the discharger 5 including a pair of rollers 7 and 8. The vacuum type paper conveyor 4 includes a vacuum producing casing 9 and a belt 10 wound around the casing 9 to draw a sheet of copying paper to the belt and convey it. The conveyor 4 is disposed so as to face the body front 2a which has a paper inlet 2b extending widthwise of the paper conveyance passageway A so as to permit insertion of a few of various sized sheets of copying paper 11, 12. The image fixing apparatus 1 uses the heating unit 3, so that when paper jamming occurs in the paper passageway A, the sheet may scorch. In order to cope with this, jam sensors 13 are disposed at the center of the width of the conveyor passageway A so that a jam detection signal from each sensor 13 may stop the operation of the image fixing apparatus 1 to thereby permit removal of the sheet of copying paper which has jammed. In FIG. 1, reference numeral 14 denotes a stock plate which accommodates thereon a sheet of copying paper 15 after fixing.
In this image fixing apparatus 1, jam sensors 13 are disposed only at the center of the width of the paper passageway A. When a wide sheet of copying paper 12 passes over jam sensors 13 and jams, this jamming will be detected, so that there are no problems Especially, when a narrow sheet of copying paper 11 is inserted from right-hand or left-hand end portion of the inlet 2b, as shown by a dot-dashed line, it does not pass over the jam sensors 13, so that when the sheet 11 jams, the jam sensor 13 cannot detect it and the sheet of copying paper within the body 2 may scorch. Such a problem could be solved by disposing many jam sensors 13 over the overall width of the sheet passage A. However, such provision of many jam sensors 13 would invite an increase in the number of components of the apparatus to thereby reduce the productivity and increase the cost. It is virtually impossible to dispose many jam sensors 13 over the paper conveyance passageway A having a narrow space.
It is an object of this invention to provide an image fixing apparatus which detects jamming of one of various sized sheets of copying paper to prevent scorching of the sheets.
It is another object of this invention to provide an inexpensive, high-productivity image fixing apparatus which is obtained by addition of a few parts to the conventional apparatus and which detects jamming of one of various sized sheets of copying paper to prevent scorching of the sheet.
Other objects and advantages of this invention will be easily ascertained by the following detailed description and accompanying drawings.